HOW DO YOU FIND THEM

A faster technique for finding intake manifold vacuum leaks is to get a bottle of propane and attach a length of rubber hose to the gas valve. Open the valve so you have a steady flow of gas. Then hold the hose near suspected leak points while the engine is idling. The resulting “correction” in the engine’s air/fuel ratio should cause a noticeable change in idle speed and/or smoothness.

CAUTION:

You could use aerosol carburetor cleaner as well.

Solvent is extremely flammable, so do not smoke or use it if there are any sparks in the vicinity (arcing plug wires, for example). Spray the solvent on suspected leak points while the engine is idling.

The idle speed will suddenly change and smooth out.

vacuum readings

TIP:

If you have a scan tool, look at the Short Term Fuel Trim (STFT) value while you are using carb cleaner or propane to check suspected vacuum leaks points.

When the cleaner or propane is sucked in through the leak, you will see a momentary drop in the STFT reading.

This confirms you have found a vacuum leaks (keep checking because there may be multiple leaks!).

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